all games: Add ConVars for changing the Steam overlay notification toasts position

[copperpixel]

Description

This PR adds ConVars that allow the player to customize the position of Steam overlay notification toasts. It does this by using the Steam API functions:

• ISteamUtils::SetOverlayNotificationInset
• ISteamUtils::SetOverlayNotificationPosition

This is also present in Counter-Strike 2.

	Description
cl_steam_overlay_toast_position	Which corner the Steam overlay notification toast should display itself in. 0 = k_EPositionTopLeft, 1 = k_EPositionTopRight, 2 = k_EPositionBottomLeft, 3 = k_EPositionBottomRight
cl_steam_overlay_toast_inset_horizontal	Steam overlay notification toast horizontal inset
cl_steam_overlay_toast_inset_vertical	Steam overlay notification toast vertical inset

Inset is specified as a percentage from 0.0 to 1.0. Steam clamps the inset to a maximum of 25% of the screen's width/height. It would also be a good idea to add these vars to the advanced settings menus of the games.

https://github.com/user-attachments/assets/7ca2f5d6-5fed-46af-8021-452f3662fb61

Closes:

• https://github.com/ValveSoftware/Source-1-Games/issues/3816